Abstract
We report on half-integer Shapiro steps observed in an InAs nanowire Josephson junction. We observed the Shapiro steps of the short ballistic InAs nanowire Josephson junction and found anomalous half-integer steps in addition to the conventional integer steps. The half-integer steps disappear as the temperature increases or transmission of the junction decreases. These experimental results agree closely with numerical calculation of the Shapiro response for the skewed current phase relation in a short ballistic Josephson junction.
Highlights
The applied DC (AC) Josephson effect has long been studied as a manifestation of macroscopic quantum interference [1] as well as for application in the quantum voltage standard [2] and more recently development of superconducting qubits [3,4]
From measurements of the gate voltage and temperature dependences of the Shapiro steps, the origin of half-integer steps is assigned to the skewness of the current phase relation in the short ballistic Josephson junctions
A Josephson junction is fabricated on a self-assembled InAs single nanowire, which is placed on a Si substrate
Summary
The AC Josephson effect has long been studied as a manifestation of macroscopic quantum interference [1] as well as for application in the quantum voltage standard [2] and more recently development of superconducting qubits [3,4]. In the case of superconductor (SC)-ferromagnet-SC junctions, the CPR holds huge higher-order components only in the vicinity of the 0-π transition temperature or thickness and the half-integer steps appear only in the vicinity [18,19,20]. When the Josephson junctions of the semiconductor nanowires are ballistic but not topological, the CPR is highly skewed [28,29]; the fractional steps are expected, they have not yet been observed experimentally. We control the junction transmission by the gate voltage of the nanowire and conclude that the half-integer steps are assigned to the skewness of the CPR appearing in the short ballistic Josephson junctions. Our numerical calculation for the short ballistic junction CPR reproduces the half-integer steps and agrees closely with the experiments, including the temperature and gate voltage dependences of the half-integer steps
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